1. Field of the invention
This invention concerns the manufacture of plate glass by flotation and especially the preparation by melting, refining, and homogenization of the glass composition to be poured on the flotation bath.
2. Background of the Prior Art
One of the problems encountered in the manufacture of plate glass by flotation is the homogenization of the glass composition suitable for being poured onto the molten metal bath of the flotation furnace, in particular when the flotation furnace operates with taps close to the maximum capacity, especially to produce colored glass. When the homogenization is not very good, streaks and waves are observed in the manufactured pane of glass. The problem of homogenization is further accentuated during changeovers from one type of glass to another, i.e., during a change of color. Poor homogenization of the poured glass composition substantially increases the time of changeover during which the glass is transformed into cullet.
Several solutions have already been proposed to solve this problem of homogenization of the glass composition to be poured. Thus, it has been proposed to introduce mechanical or thermal baffles into the melting tank to force the flow of glass to pass through openings deep in the glass bath.
It has also been proposed to produce a mixing of molten glass by agitators. For example, in the publication of the French Certificate of Addition No. 2 287 423, it has been proposed to mix the molten glass using vertical agitators traversing the arch of the furnace.
This device, effective as far as the homogenization of the glass is concerned, is complicated to implement. Its maintenance is also difficult since the mechanical parts of which it is composed operate above the arch of the furnace and accordingly at high temperature, and deteriorate rapidly.
In the publication of the French Patent FR-A-2 213 914, a process is described by which the flow of molten glass is modified in the refining region, and starting from it toward the working region, also called the homogenization zone or live coal zone, to improve the homogeneity of the glass by causing a cooling liquid to flow in one or more pipes that extend substantially horizontally across at least a portion of the tank in the upper region of the molten glass, at the junction of the refining region with the working region, or close to it, and causing a transverse horizontal displacement of the molten glass in the glass stream by displacement according to a back and forth motion of the pipe or pipes. The effectiveness of this device is not entirely satisfactory, and the changeover times in particular remain long.
In the publication of French Patent FR-A-792 996, horizontal agitation is also described, using an arm provided with several fingers of cylindrical shape. The efficacy of this device is not entirely satisfactory.
None of these known devices provide complete satisfaction. They are difficult to utilize or have dubious effectiveness.